I’ve forgotten what your Connexx fitting profile looks like with any feedback sensitivity region displayed. For me, I found the most useful curve was the feedback analysis curve provided by ReSound’s Smart Fit software. It showed, for example, that even with an “oversized” tulip dome or a power dome crammed into my ear canal that, because of the irregularities in the shape of the canal that one is trying to occlude with a pretty regularly-shaped device, the inexpensive, off-the-shelf domes were just not allowing me to control occlusion to whatever degree that I wanted. As expected, when I switched to custom-made molds by inserting a solid vent insert, if I wanted, I can get almost 100% complete occlusion. One of my ear canals is very small and it requires a pretty small mold that just accommodates the receiver and the vent tube. I know some users have mentioned getting their custom molds with money-back guarantees - maybe they were already paying a provider for the full retail package? - but I wonder if your provider could tell just from inspection or just making an impression (hopefully cheaper than completing the deal with a mold) whether your ear canal will accept a suitably sized mold made to use select-a-vent?
See Smart Fitting curves towards the bottom of the following post. The light gray shaded area descending from the top of each graph shows the region sensitive to feedback (hence the lack of occlusion) below the amplification max limit for the receiver in use (MP in my instance) (lower limit of top pinkish red region).